From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id C415EC75 for ; Thu, 19 Sep 2019 15:15:05 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40135.protonmail.ch (mail-40135.protonmail.ch [185.70.40.135]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 134618B0 for ; Thu, 19 Sep 2019 15:15:05 +0000 (UTC) Date: Thu, 19 Sep 2019 15:15:00 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1568906102; bh=A5jzuoGM7fmVXWFmZrlJWcUkVq0ebz6lfkfaa5olvNY=; h=Date:To:From:Reply-To:Subject:In-Reply-To:References:Feedback-ID: From; b=OhDxJw5l/ML0xgeg/hBHoDTfCsfhE9mAxI9VJhOLGgh62AKO7AJF4K0hw08du3OcP ke+t56FEZF9OoRXM06TqF+C4m9O6zJWOnUhshvp+lpo94EkZS5A4W+CFKVA88k2GwL 72Lzy/S9m7LZ5/4Q8so+YK1qwNcAhOPn7C5bMlZE= To: John Tromp , Bitcoin Protocol Discussion From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: In-Reply-To: References: Feedback-ID: el4j0RWPRERue64lIQeq9Y2FP-mdB86tFqjmrJyEPR9VAtMovPEo9tvgA0CrTsSHJeeyPXqnoAu6DN-R04uJUg==:Ext:ProtonMail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, FROM_LOCAL_NOVOWEL, RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Subject: Re: [bitcoin-dev] Timelocks and Lightning on MimbleWimble X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 Sep 2019 15:15:05 -0000 Good morning John, > > However, I believe that Lightning and similar offchain protocols are no= t possible on MimbleWimble, at least if we want to retain its "magical shri= nking blockchain" property. > > MimbleWimble can easily incorporate relative lock heights, in addition > to absolute lock heights. Grin and Beam have included the latter since > launch. > > Grin's proposal for relative lock heights is at [1] with discussion at [2= ]. > Based on these, Grin also has a rough design for payment channels at [3]. > > Beam included relative lock heights in its recent HardFork [4] and has > a payment channel design at [5]. > Thank you for this information. I am aware that absolute locktimes were possible in MimbleWimble. However, it does seem to imply that kernels are not compressible (unlike th= e original MimbleWimble where the kernel is just an empty string and thus n= ever stored). So at least for kernels of relative locktimes, are not pruneable and will c= ontribute to blockchain size. (I believe I saw some proposal for absolute locktimes that allow some amoun= t of aggregation/pruning of absolute-locktime kernels from the mimblewimble= .pdf by andytoshi.) Which I suppose is my point: you lose some of the "magic shrinking blockcha= in" property in implementing relative locktimes, as you now increase the da= ta you have to store forever (i.e. the kernels). It is not a *total* loss of the "magic shrinking blockchain", I see now, ho= wever. Still, it does see worth the cost of accepting having to store kernels fore= ver in exchange for being able to layer on top of a MimbleWimble blockchain= . It seems to me that Poon-Dryja and Decker-Wattenhofer can be "directly" por= ted over to any MimbleWimble blockchain with relative locktimes. Reference [5] seems to be Poon-Dryja ported over to using relative locktime= s for MimbleWimble. Decker-Russell-Osuntokun ("eltoo") is harder due to the `SIGHASH_NOINPUT` r= equirement. I have tried to derive an equivalent to this `SIGHASH_NOINPUT` somehow by c= onsidering that the "reference to previous kernel" as being akin to the Bit= coin transaction input referring to a previous output, however it seems to = be not easy to create a retargatable "reference to previous kernel" in this= way. In any case, it seems to me that the loss of SCRIPT does not prevent a Mimb= leWimble blockchain from using an offchain updateable cryptocurrency system= . Regards, ZmnSCPxj